Wound and tissue injuries are common medical problems that often lead to excessive scar formation and subsequent loss of organ function without normal tissue replacement. Understanding the molecules that control scarless regenerative healing can provide a means to modulate healing and mitigate these significant threats to public health. We have demonstrated previously that adult MRL mice show unique scarless and regenerative-type healing. In these mice, through-and-through ear hole wounds close completely, whereas those in other mice scar. Ear wounds of MRL mice display re-growth of cartilage and hair follicles. In addition, following cryoinjury to the right ventricle of the heart, we have shown healing occurs without scarring, with nearly complete replacement of cardiomyocytes, and with return to normal function. We have also demonstrated that the ear hole closure phenotype is controlled by multiple genetic loci, is a complex quantitative trait, and is profoundly influenced by sex. Based on these observations, we propose to identify the genes that regulate regenerative healing in mice using a combination of linkage mapping and gene expression profiling. The inbred MRL mouse strain derives from the LG mouse strain, which is the only other strain shown to have this regenerative capacity. An advanced intercross line (AIL) and a large panel of recombinant inbred (Rl) strains between LG/J (Large) and SM/J (Small) mice has been constructed that provides us the unique means to examine their regenerative healing, to explore the full range of their phenotypes, and to map the regeneration genes in these MRL progenitors. In this proposal, a consortium of four, laboratories will carry out phenotyping, genotyping, gene expression studies, and in vitro wound healing assays. The specific aims are: 1. Generating 500 LGXSM F2 mice for initial QTL mapping and 1000 LGXSM AIL for fine mapping;2. Sub-phenotyping ear hole closure and analyzing in vitro wound healing using fibroblasts, endothelial cells, and keratinocytes;3. Studying gene expression by comparing cells and ear tissue that display differential healing properties. Although synergistic, these specific aims can be accomplished independently of each other to provide significant information. Our study of regenerative healing using the well-defined LGXSM mouse resource enables us to realize the promising potential of this genetically powerful and unique healing model system.